Within the ventral spinal cord there resides a diverse population of interneurons (INs) that play important roles in regulating the activity of motor neurons during locomotion. A screen for novel IN markers has revealed the presence of a previously unknown class of lamina VIMINs that arise at the boundary between d!6 and VOINs. These INs specifically express the transcription factor WT1, which is an important developmental regulator of a number of organ systems. The work proposed here will utilize the restricted expression of WT1 in the spinal cord to characterize this newly identified class of INs, providing insight into their contributions to spinal cord function. Additionally, these INs will be inactivated to directly test their role in locomotor behavior. The proposed studies will provide insight into the spinal cord circuitry controlling locomotor behavior and the developmental processes involved in the generation of functionally distinct spinal cord neurons. The techniques used will include marker expression analysis, dextran fills, pseudorabies virus injections, electrophysiology in reduced spinal cord preparations, gene targeting, allatostatin-mediated silencing of neuronal activity, and behavioral analysis.